1. Field of the Invention
The present invention relates to an information recording medium in which information is recorded on a recording film using laser light and in which information recorded on the recording film is reproduced or erased, as well as an information reproduction apparatus for reproducing information recorded on the information recording medium, and in particular, to an information recording medium and an information reproduction apparatus that enable high density information to be recorded.
2. Description of the Prior Art
Magneto-optical discs and DVD-RAMs are known as information recording media in which information is recorded on a recording film using laser light and in which information recorded on the recording film is reproduced or erased.
The conventional information recording medium is composed of land portions on which information is recorded and groove portions each separating a land portion from the adjacent land portion, wherein the land and groove portions form an irregular pattern. The land and groove portions each form one track, which is divided into several tens of sectors. Pits called xe2x80x9cpreformat pitsxe2x80x9d indicating the track number of each sector are formed at the head of the sector.
If the track pitch (the interval between the land and groove portions) is reduced in order to improve the density of information recorded on the information recording medium, crosstalks (when information recorded on a certain track is to be reproduced, information recorded on the adjacent track is simultaneously read) may increase.
Japanese Patent Laid-Open No. 1-286122 and Japanese Patent Laid-Open No. 5-166739 specifications disclose methods for reducing crosstalks.
The method disclosed in Japanese Patent Laid-Open No. 1-286122 specification arranges adjacent preformats in such a way as to be alternately offset from one another.
The method disclosed in Japanese Patent Laid-Open No. 5-166739 specification forms preformats convex from recording tracks.
In addition, the land groove recording method for recording information on both the land and groove portions is favorable in improving the density of information recorded on an information recording medium. K. Kayanuma et al have reported the effectiveness of this method (SPIE Proceedings Vol. 1316, p.35).
The method for recording information on both the land and groove portions has already been employed for DVD-RAMs. In the VD-RAM, the preformat pits are formed on the extension of the boundary between the land and groove portions. FIG. 19 is an enlarged view of a preformat portion in the DVD-RAM showing an arrangement of preformat pits. As shown in FIG. 19, the preformat pits are formed in a flat portion in which the groove of the groove portion is discontinued, and four preformat pits are formed for one sector. Specifically, four preformat pits A1, A2, B1, and B2 are formed for the concave (groove) sector, while four preformat pits A3, A4, B1, and B2 are formed for the adjacent convex (land) sector. The two preformat pits formed on the extension of the boundary between the concave and convex portions are shared by the adjacent concave and convex sectors.
Even in such an information recording medium based on the land groove recording method, if the track pitch is reduced in order to improve the recording density, crosstalks may increase, thereby making it difficult for precluding good preformat pits to be formed.
Japanese Patent Laid-Open No. 9-73635 and Japanese Patent Laid-Open No. 9-147366 specifications disclose methods for reducing crosstalks.
The method disclosed in Japanese Patent Laid-Open No. 9-73635 specification forms preformat pits for both the land and groove portions and pairs two adjacent tracks so that the arrangement of pre-pits is the same within each of the pairs while it is different between adjacent pairs in order to reduce the extent to which a laser spot used to reproduce information is applied on the pre-pits for the adjacent track. Moreover, the polarity of signals of the pre-pits is reversed between adjacent pairs in order to reduce crosstalks in the preformat portion.
The method disclosed in Japanese Patent Laid-Open No. 9-147366 specification reduces crosstalks by comparing the amount of light reflected from wobble pits arranged at positions prior to an identifying signal section and on the right and left side of the center line of a track to increase the accuracy of track follow-up control for the laser spot in order to avoid off-tracks. In addition, the wobble pits are located at positions followed and preceded by a synchronizing signal section and the identifying signal section. Processes carried out by a reproduction apparatus occurs at space or time interval between the detection of a synchronizing signal and the detection of a signal from the wobble pits and between the detection of the signal from the wobble pits and the detection of an identifying signal. A certain interval is provided before and after the wobble pits corresponding to a distance over which the laser spot advances while the reproduction apparatus is executing the above processing. The off-track means that the laser spot scanning deviated from the track from which information is being reproduced due to the decentering of an information recording medium itself or a rotating shaft of a motor rotating the information recording medium during information reproduction. When the off-track occurs, the area of preformat pits covered by the laser spot may be reduced causing to decrease the intensity of information reproduced.
As described above, in the DVD-RAM, when the track pitch is reduced in order to improve the density of information recorded, crosstalks or off-tracks may increase.
In addition, the method disclosed in Japanese Patent Laid-Open No. 9-73635 specification reduces crosstalks but cannot avoid the decrease in the level of reproduced signals caused by off-tracks.
Also, the method disclosed in Japanese Patent Laid-Open No. 9-147366 specification executes processing for the follow-up control for the laser spot. But this method must provide the interval for this processing in the preformat portion. Consequently, the area of the preformat portion increases to reduce the sector utilization.
An object of this invention is to solve these problems and to provide an information recording medium and an information reproduction apparatus that allow the capacity for information recorded to be increased easily.
To attain this object, an information recording medium according to a first aspect of this invention is characterized by comprising a preformat pit array existing on the extension of the boundary between adjacent recording tracks and containing information on both recording tracks sandwiching the boundary, and an adjustment pit existing at a position prior to the preformat pit array relative to the advancing direction of light that reproduces recorded information, adjusting the signal level of a reproduced signal from the preformat pit array.
This aspect of the invention can correct the reproduced signal from the preformat pit array so as to have a signal level required to accurately reproduce information, based on the signal level of the reproduced signal from the adjustment pit array. Thus, the information recorded on the preformat pit array and subsequent sector can be reproduced correctly.
The adjustment pit may be formed at the extension of the boundary between adjacent tracks same as in the case of the preformat pit array or on the extension of an adjacent boundary and may be a single or a plurality of pit arrays.
An information reproduction apparatus according to a second aspect of this invention is characterized by comprising a preformat pit array existing on the extension of the boundary between adjacent recording tracks and comprising information on both recording tracks sandwiching the boundary, and an adjustment pit existing at a position prior to the preformat pit array relative to the advancing direction of light that reproduces recorded information, existing on both the extension of the boundary same as in the case of the preformat pit array and the extension of an adjacent boundary, adjusting the signal level of a reproduced signal from the preformat pit array.
This aspect of the invention can show how the center of light is deviated from the center line of a track, based on the signal level of the reproduced signal from the adjustment pit array. By correcting the reproduced signal from the preformat pit array that has been varied due to this offset, so as to have a signal level required to reproduce information correctly, this aspect of the invention can correctly reproduce the information recorded on the preformat pit array and subsequent sector.
The adjustment pit may comprise a single pit or an array of continuous pit array.
An information reproduction apparatus according to a third aspect of this invention is an information reproduction apparatus for reproducing information recorded on an information recording medium according to the first and second aspects of this invention, characterized in that a reproduction means for photoelectrically transforming light from the information recording medium to reproduce a signal recorded on the information recording medium, an amplifying means for amplifying the signal reproduced by the reproduction means, a level determining means for detecting the reproduced signal coming from the adjustment pit array, out of the output signal from the reproduction means in order to determine the signal level of this reproduced signal, and an amplifying rate adjustment means for adjusting the amplifying rate of the amplifying means according to the signal level determined by the level determining means and outputting the reproduced signal from the preformat pit array at a certain signal level.
This aspect of the invention can also correct the reproduced signal from the preformat pit array so as to have a signal level required to accurately reproduce information, based on the signal level of the reproduced signal from the adjustment pit array. Thus, the information recorded on the preformat pit array and subsequent sector can be reproduced correctly.
The amplifying means may amplify the sum of the signal levels of signals reproduced by a plurality of the reproduction means or the difference between the signal levels of signals reproduced by a plurality of the reproduction means.
An information reproduction apparatus according to a fourth aspect of this invention is an information reproduction apparatus for reproducing information recorded on an information recording medium according to the first and second aspects of this invention, characterized by comprising a reproduction means for reproducing signals recorded on the information recording medium, from light from the information recording medium, an amplifying means for amplifying the signals reproduced by the reproduction means, a level determining means for detecting from the output signals from the reproduction means the reproduced signals from the adjustment pit array existing on the extension of the boundary between adjacent tracks same as in the case of the preformat pit array and on the extension of an adjacent boundary in order to determine the signal level of each reproduced signal, and an amplifying rate adjustment means for adjusting the amplifying rate of the amplifying means according to the signal level determined by the level determining means and outputting the reproduced signals from the preformat pit array at predetermined signal levels.
This aspect of the invention can also show how the center of light is deviated from the center line of a track, based on the signal level of the reproduced signal from the adjustment pit array. By correcting the reproduced signal from the preformat pit array that has been varied due to this offset, so as to have a signal level required to reproduce information correctly, this aspect of the invention can correctly reproduce the information recorded on the preformat pit array and subsequent sector.
The level determining means may determine the signal levels of the reproduced signals from the adjustment pit array existing on the extension of the boundary between adjacent tracks same as in the case of the preformat pit array and on the extension of an adjacent boundary, based on the sum of the signal levels of signals reproduced by a plurality of the reproduction means or the difference between the signal levels of signals reproduced by a plurality of the reproduction means.
The amplifying means may amplify the sum of the signal levels of signals reproduced by a plurality of the reproduction means or the difference between the signal levels of signals reproduced by a plurality of the reproduction means.